The invention disclosed herein pertains to a reference electrode having an immobilized electrolyte which makes electrical contact with a reference element and can be brought into contact with a test solution which is to be measured either directly or through a bridging electrolyte. The reference electrolyte and, if present, the bridging electrolyte is immobilized by means of an hydraulically setting inorganic cementitious material, that is, an aqueous solution of the electrolyte is mixed in the material before it sets.
It is known to reduce maintenance costs and improve operation of reference electrodes by immobilizing the electrolyte. To achieve immobilization, the reference electrolyte is generally a sodium or potassium chloride solution densified with a natural or synthetic polymer to obtain various degrees of stiffness. German application DE-PS 9 39 597 describes a low maintenance reference electrode which contains a potassium chloride electrolyte gel. The gel contains air bubbles which are intentionally included in order to allow compensation for the great differences in thermal expansion between the gel and the material composing the electrode body due to temperature variations whereby bursting of the electrode body is avoided. When there is expansion and compression of air bubbles at a constant temperature but with changing pressure, the measuring solution can be forced through the diaphragm of the electrode into the reference electrolytes and, especially in the presence of substances toxic to the electrodes, undesirable alteration of the reference potential may occur.
In German Patents DE OS 323 28 647 and DE PS 34 05 431 reference electrodes are described which are filled with gelled reference electrolytes in which there are no air bubbles.
These reference electrodes are suited for use with changing pressures but they are not well suited for use under changing temperature conditions. In these electrodes, bursting of the electrode body is avoided by providing the body with an opening through which, when a positive temperature is developed, the gelled electrode can escape to relieve the pressure. But if the temperature is lowered, the gel again contracts so an undesirable pumping effect occurs which can extend to the electrode body by means of a measuring solution and sooner or later leads to a reference electrode that will not operate.